The use of heat exchangers to cool lubricating oil employed in an internal combustion engine has long been known. One form of such heat exchangers currently in use is a so-called "donut" oil cooler. These oil coolers have an axial length of only a couple of inches or less and are constructed so that they may be interposed between the engine block and the oil filter, being attached direct to the block in a location formerly occupied by the oil filter.
Typically, oil coolers of this type include a multi-piece housing which is connected to the vehicular cooling system to receive coolant, and which contains a stack of relatively thin, disc-like chambers through which the oil to be cooled is circulated. It is common for the upper end of the heat exchanger to be defined by a stamped, sheet metal filter plate that is shaped to provide an annular peripheral chamber or dome which serves as a stabilizing mount for the oil filter when the filter is mounted to the heat exchanger. Normally, there is a central opening through the oil cooler through which a connector extends to attach the oil cooler to the engine block and the oil filter to the oil cooler.
It is also common, in such oil coolers, to employ bypass valves to allow the oil to bypass the disc-like chambers when the oil is at a high viscosity, as when cold, and obviously not in need of further cooling in the heat exchanger. This prevents both a large pressure drop in the oil as it passes through the heat exchanger to the filter and the over pressurization of the oil cooler housing.
Typically, this bypass function is provided by a spring-biased poppet valve or a sheet metal flapper valve placed in the oil cooler between the central opening and the dome of the filter plate. Conventional flapper valves have a biasing spring that is located and contained by the interior of the dome of the filter plate, with a flapper extending inwardly towards the central opening. Conventional spring-biased poppet valves are inserted in the available area between the central opening and the dome. Both types of valves work well for their intended purpose.
However, due to current efforts in the automobile industry to increase fuel efficiency, there have been changes in the construction of the oil coolers which are incompatible with these conventional types of bypass valves.
One of the changes in construction involves an adaptation to allow the oil cooler to mate with larger diameter, higher flow capacity oil filters. Increasing the diameter of the oil filter, rather than the length, allows for higher capacity filters to be installed in engine compartments without requiring room for additional length. Due to their stamped sheet metal configuration, conventional domed filter plates are limited as to the diameter of oil filter with which they can mate. One solution to this problem has been to replace the conventional domed plate with a flat, solid filter plate having a sealing surface that extends to the outermost diameter of the oil cooler. This allows the oil cooler to be mated with several different diameters of oil filters, including filters with diameters that approximate the diameter of the oil cooler.
However, the use of the solid filter plate prevents the oil cooler from using a conventional flapper pressure relief valve. As noted earlier, conventional flapper valves require a dome/annular chamber for location and constraint. Further, spring-biased poppet valves require additional oil cooler length, which is undesirable in oil coolers designed for use with large diameter filters. Additionally, some users of such oil coolers are hesitant to employ spring-biased poppet valves, due to reliability concerns related to multipart components.
Thus, it can be seen that there is a need for a new and reliable bypass pressure relief valve which can be incorporated within an oil cooler having a solid, flat filter plate.